Gemini 11: Preparing for Apollo

The year 1966 was a pivotal one in the race to reach the Moon. Testing of the Apollo spacecraft in preparation for the first manned flight in early 1967 was in full swing (see “AS-202: The Last Test Flight Before Apollo 1“) and the Saturn 500F, a non-flight version of NASA’s Saturn V Moon rocket, was already being used to check out the new facilities at Launch Complex 39 during the summer of 1966 (see “The Saturn 500F: The Moon Rocket That Couldn’t Fly“).  During the first half of 1966, NASA had also flown a fast-paced series of manned missions as part of the Gemini program to test the technologies and learn the skills needed for Apollo to reach the Moon. While there were some problems encountered and some set backs especially during EVAs (extravehicular activities), the first three Gemini missions of 1966 managed to test a variety of rendezvous and docking techniques that were essential to Apollo. The second-to-last Gemini mission, the flight of Gemini 11, would continue the push up the learning curve as preparations for Apollo continued.

 

Gemini Program Objectives

The purpose of NASA’s Gemini program was to develop the technologies and techniques needed to fulfill President Kennedy’s goal of landing a man on the Moon by 1970. The major objectives of the program were:

– Demonstrate that humans and their equipment can survive up to two weeks in space
– Demonstrate rendezvous and docking techniques in orbit
– Demonstrate the technology and techniques needed to perform EVAs (Extra-Vehicular Activities)

Meeting all of these objectives was necessary if the Apollo lunar program were to be successful.

Gemini was a two-man spacecraft that was roughly conical in shape with a base diameter of 3.3 meters which stood 5.8 meters tall.  Built by the McDonnell Aircraft Corporation (which merged with Douglas in 1967 to become McDonnell Douglas which subsequently merged with Boeing 30 years later), it consisted of two major sections. The first section was the reentry module which housed the crew, their equipment, food supplies and so on in orbit as well as the recovery systems needed to safely return them to Earth. The nose of this module also contained an L-band radar system for orbital rendezvous operations. Unlike today’s crewed spacecraft, the Gemini crew cabin was pressurized with pure oxygen at about one-third standard atmospheric pressure to save weight. The next section, the adapter section, connected the reentry module to the launch vehicle during ascent and housed equipment needed to support the crew while in orbit. It consisted of a retrograde section which held a set of four solid retrorockets used to start the descent to Earth from orbit and an equipment section which housed the in-orbit propulsion system called OAMS (Orbital Attitude and Maneuvering System), life support, power systems and all other equipment not needed for the return to Earth.

With a typical launch mass of up to about 3,700 kilograms or more, Gemini needed the largest operational rocket available at the time to get into orbit: a modified Titan II ICBM built by Martin Marietta (which is now part of Lockheed Martin). A number of modifications were made to simplify the operation of this rocket, smooth out its ride and improve its reliability to support crewed missions. With the Gemini spacecraft mounted on top, the Titan II GLV (Gemini Launch Vehicle) was 33 meters tall and had a fully fueled launch mass of about 154 metric tons.

Since its first manned mission in March 1965, the Gemini program had made steady progress in meeting its objectives in support of Apollo over the following 18 months. A series of three long duration missions culminating in the two-week flight of Gemini 7 in December 1965 demonstrated that a crew and its spacecraft could operate in space for periods of time longer than that needed for Apollo to land on the Moon and return (see “Gemini 7: Two Weeks in the Front Seat of a Volkswagen“). With this major program objective met, the rest of the Gemini missions concentrated on perfecting rendezvous and docking techniques as well developing the skills needed to perform EVAs.

Gemini 6 successfully performed the first rendezvous using Gemini 7 as a target (see “Rendezvous in Space: Gemini 6 and 7”). Gemini 8 completed the first docking in orbit in March 1966 although its mission was cut short due to a thruster malfunction (see “Gemini 8: The First Docking in Space”). Gemini 9 attempted to repeat the feat of its predecessor in June with a faster and more aggressive rendezvous profile but was unable to dock with its target because its launch shroud had failed to jettison properly (see “The Angry Alligator & The Snake: The Mission of Gemini 9”). Difficulties were also encountered during the mission’s EVA forcing it to be cut short due to astronaut fatigue. Building on the experience of the earlier missions, Gemini 10 not only rendezvoused and docked with its Agena target vehicle, but used the stage’s propulsion system to boost the combined craft to a record setting altitude. Gemini 10 then successfully performed a rendezvous with a second target – the derelict Agena used earlier during the Gemini 8 mission. A pair of EVAs were also performed during this mission with mixed results (see “Gemini 10: Dual Rendezvous in Space”). The objectives of the Gemini 11 mission were to continue gaining experience in rendezvous and docking in support of the Apollo program as well as addressing the ongoing EVA issues.

 

The Gemini 11 Mission Plan

On March 21, 1966 NASA named the crew for the Gemini 11 mission. The primary crew consisted of USN Commander Charles “Pete” Conrad, Jr. as the command pilot and USN Lt. Commander Richard F. Gordon, Jr. as the pilot. Conrad was 36 years old and had been a Navy test pilot and flight instructor before being selected as part of NASA’s second group of astronauts in September 1962 (see “NASA Selects the ‘New Nine’ – September 17, 1962“). He had previously flown as the pilot on the eight-day Gemini 5 mission with Gordon Cooper in August 1965 (see “Eight Days or Bust: The Mission of Gemini 5”). Gordon, like Conrad, was also 36 years old and had served as a Navy test pilot as well as a flight instructor before being selected as part of NASA’s third group of astronauts in October 1963. This would be his first spaceflight. The backup crew for the Gemini 11 mission consisted of veteran civilian astronaut Neil A. Armstrong as the command pilot and rookie astronaut USAF Captain William A. Anders as the pilot.

Like the previous three missions, the first set of objectives for the Gemini 11 mission centered on orbital rendezvous and docking. The docking target chosen for the Gemini program was a modified Agena D upper stage known as the Gemini Agena Target Vehicle (GATV) launched into orbit using the SLV-3 (Standard Launch Vehicle-3) version of the Atlas booster built by General Dynamics. Built by the Lockheed Missile and Space Company (which is now part of the aerospace giant, Lockheed Martin), the Agena D not only served as an upper stage for use with Thor, Atlas, and Titan IIIB rockets, but had also been integrated into range of Defense Department payloads such as the Corona reconnaissance satellites to provide in-orbit support functions during these missions. The standardized Agena D, with its adaptable modular design, could be easily modified to serve as a docking target for Gemini.

In addition to modifications to its primary and secondary propulsion systems to support its role as a docking target, the forward end of the Agena D was fitted with an auxiliary rack holding special rendezvous and telemetry equipment. Also added were strobe lights and an L-band radar transponder to aid in rendezvous operations as well as command equipment to allow the GATV to be controlled from the ground or by the Gemini crew. A cone shaped target docking adapter (TDA), which was under a shroud during launch, was added to the forward end of the stage to allow the nose of the Gemini reentry module to dock with the Agena and mechanically lock the two spacecraft together. Once in orbit, the GATV was 9.7 meters long with a mass of about 3,200 kilograms.

A number of different rendezvous modes with the GATV had been identified during theoretical studies of the technique. For the Gemini rendezvous missions, the “coelliptical” method was chosen where the active spacecraft would first be placed into a circular orbit below and some distance behind the passive target spacecraft. The active spacecraft would then catch up to its target over the course of several orbits then maneuver to match the target’s orbit in order to perform the actual docking. While this approach took longer than other possible profiles, it was much more flexible and allowed more time to plan and execute maneuvers – a desirable characteristic for the first attempts of the untried procedure of orbital rendezvous. Ultimately it was decided that the Apollo Lunar Module (LM) would follow a similar rendezvous profile as it returned to orbit following launch from the lunar surface.

In the case of the Gemini 6, 8 and 10 flights, the crew followed what was called a “M=4” rendezvous profile where the initial rendezvous took place during the fourth revolution after launch. The Gemini 9 mission followed a faster M=3 rendezvous which better approximated the desired rendezvous procedure for the LM. This was accomplished by the crew performing an IVAR (Insertion Velocity Adjust Routine) maneuver of up to 9 meters per second right after separating from their spent Titan II launch vehicle to reduce the inevitable orbit insertion errors using data provided by the spacecraft’s guidance system. After this, the Gemini 9 crew combined what had been several individual orbit adjustments performed over the course of a couple of revolutions into a single maneuver to reduce the time to rendezvous.

Ultimately Apollo mission planners wished to follow an M=1 profile where the LM would rendezvous during the first orbit after leaving the Moon. After much debate, it was decided to test this highly aggressive flight profile on the Gemini 11 mission to gauge the workload on the crew. Since the spacecraft would be out of touch with ground controllers during many of the key events of the rendezvous, the astronauts would rely solely on their own instruments and calculations performed on board by their guidance computer to execute a comparatively rapid series of highly precise maneuvers. The final docking would take place before the end of the first orbit as the two spacecraft approached the continental US. Afterwards, Conrad and Gordon would take turns undocking and redocking with the Agena target to gain additional experience on this important procedure.

The second day of the Gemini 11 mission would be dominated by activities associated with the mission’s first EVA (extravehicular activity). Although America’s first EVA performed by Ed White in June 1965 during the Gemini 4 mission went largely without incident (see “The Forgotten Mission of Gemini 4”), difficulties encountered during the EVAs performed as part of the Gemini 9 and 10 missions resulting in astronaut fatigue as well as other issues demonstrated that changes were needed in EVA procedures, equipment and training. Basically, more experience with shorter EVAs focused on fewer objectives was necessary to learn what was needed.

While still docked to the Agena, Dick Gordon was scheduled to perform a series of tasks during his first EVA while attached to the Gemini via an umbilical line which supplied oxygen and other support functions. As in earlier EVAs, Gordon would wear a modified G4C space suit and a 19-kilogram, chest mounted Extravehicular Life Support System (ELSS). The ELSS controlled his life support and provided 30-minutes of emergency oxygen if a problem arose with the ship’s supply. Because of issues with long umbilicals during the Gemini 9 and 10 EVAs, Gordon would use a shorter nine-meter line. Handrails, foot holds and other restraints would be used during this flight to address problems encountered during earlier EVAs. A Hand Held Maneuvering Unit (HHMU) like that used during earlier missions would be evaluated as would a handheld power tool for the first time in space. This first EVA was scheduled to last 107 minutes.

During the course of mission planning, Pete Conrad had pushed hard to use the Agena’s primary propulsion system (PPS) to boost the docked spacecraft into a higher, record-setting orbit as had been done during the flight of Gemini 10. Conrad argued that this higher orbit would allow him and Gordon to perform synoptic cloud photography with a higher resolution than that provided by weather satellites of the day like TIROS and Nimbus to help scientists study weather phenomena. To address concerns about enhanced radiation exposure at these higher altitudes, Conrad turned to experts including his backup pilot, Bill Anders, who had a masters degree in nuclear engineering and had practical experience in radiation effects from when he worked at the Air Force Weapons Laboratory at Kirtland AFB in New Mexico before joining NASA. With no major issues identified, the plan was approved to use the Agena on the third day of the mission to raise the apogee of the docked spacecraft to 1,392 kilometers for two orbits before returning to a circular 298-kilometer orbit for the balance of the flight.

About 46 hours into the mission, Gordon would perform a second “stand up” EVA. As the name implies, Gordon would stand up in the open hatch allowing his upper body to be exposed to space while he execute his tasks. The astronaut would perform Earth and astronomical photography during his second EVA scheduled to last 140 minutes. About an hour and a half after the scheduled end of the EVA, Gemini 11 would separate from the Agena to unfurl a 30-meter long tether connecting the two spacecraft. This tether, which would have been connected to the docking bar on Gemini’s nose during Gordon’s umbilical EVA a day earlier, would be used in stationkeeping exercises with the Agena. First, the combination would be stabilized in a gravity gradient mode with the Agena in an engine-down position with the Gemini above it with its nose pointing downwards. Later, the Gemini OAMS would be used to start a slow rotation which would generate a small amount of artificial gravity. After about three hours on the tether, pyrotechnic charges would be activated to detach the docking bar allowing the two spacecraft to finally separate.

During the following orbit, the OAMS thrusters would lower Gemini’s perigee in preparation for retro fire about 16 hours later. For the remainder of the flight, the crew would perform more experiments, take their last sleep period of the mission and then prepare for return. At a mission elapse time of 70 hours and 40 minutes, Gemini 11 would fire its retrorockets to begin the half hour descent back to Earth. One of the secondary objectives of this mission was for the Gemini reentry module to execute an automatic reentry where, for the first time during a manned mission, the computer would actively steer the craft towards its intended landing zone – a technique which could be employed by Apollo. The mission was scheduled to end with a splashdown in the West Atlantic recovery area about 1,170 kilometers east of Cape Kennedy (as Cape Canaveral was known from the end of 1963 to 1973) where the mission had started 71 hours and 5 minutes earlier.

 

Getting off the Ground

The first piece of mission hardware to arrive at Cape Kennedy was the Atlas TLV-5306 rocket to be used to launch the Agena GATV. It arrived on January 14, 1966 with the installation of mission specific equipment completed by June 20. Next, Spacecraft No. 11 arrived from the McDonnell plant in St. Louis on July 7 followed by the Titan II GLV-11 from Martin’s Baltimore facility on July 12. As testing proceeded on these pieces of flight hardware, Agena GATV-5006 was delivered three days later.

GLV-11 was erected on the pad at Launch Complex 19 (LC-19) on July 22 only four days after the launch of Gemini 10. On July 28, Atlas TLV-5306 was erected on its pad at LC-14. After completing its required testing, the GATV was mated with the Atlas on August 22 followed two days later when the Gemini was mated with its launch vehicle. Following the completion of the final simulated flight test on September 2, all was ready for the first launch attempt scheduled for September 9.

According to the original plan, the Agena target vehicle would be the first off the pad at 7:48 AM EST to be placed into a circular 298 kilometer orbit. Gemini 11 would follow as GATV-5006 was about to complete its first orbit about 97 minutes later with the precise launch time dictated by the actual orbit attained by the GATV. With only a two-second launch window (the shortest of the Gemini program), Gemini 11 would liftoff and be placed into an initial 161 by 280 kilometer orbit to start a rapid series of events to close the 396-kilometer gap to the target. As in previous missions, there were various launch windows available on subsequent days in case Gemini did not make it off the pad on this first day.

The first launch attempt on September 9, 1966 was scrubbed early in the countdown when a pinhole leak in the first stage oxidizer tank of the Titan II GLV-11 was discovered. As technicians patched the hole, the launch was recycled to the following day. Conrad and Gordon got up in the predawn hours of September 10 and started the now routine prelaunch ritual of breakfast, medical checks, suiting up in the support trailer at LC-16 and then heading off to the waiting Gemini-Titan II at LC-19. But as the astronauts were preparing themselves, ground crews tasked with the launch of the Agena GATV at LC-14 called a hold to the combined countdown to deal with an apparent problem with the Atlas’ autopilot. As technicians wrestled with this new issue, Conrad and Gordon were held in the white room at LC-19 waiting for the go ahead to get into their spacecraft when the countdown resumed. Unfortunately, at 7:10 AM EST the countdown was scrubbed after a 56-minute hold and the disappointed crew headed back down the gantry. The launch was postponed for two more days.

Once again, Pete Conrad and Dick Gordon were woken up well before dawn on September 12, 1966 for another launch attempt. After having breakfast with Alan Shepard (at the time, Chief of the Manned Space Center Astronaut Office), the crew suited up and arrived in the white room at LC-19 at 7:25 AM EST. Conrad and Gordon got a briefing on launch preparations from Armstrong and Anders who had been at the pad for hours and entered their waiting spacecraft. Although Conrad detected a leak in his hatch, technicians were able to fix the problem with only a 16-minute delay in the countdown. Two kilometers away at LC-14, Atlas TLV-5306 lifted off at 8:05:01.725 AM EST and quickly accelerated out over the Atlantic and towards orbit. After the Agena GATV-5006 shutdown its engine several minutes later, Gemini’s target was in a 284.6 by 302 kilometer orbit with a period of 90.55 minutes – just a touch longer than planned but well within mission requirements.

The countdown at LC-19 proceeded until 9:37:05 AM where it stopped for a scheduled hold at the T-13 minutes mark in order to bring Gemini’s launch time into proper phase with its Agena target. After a hold of 141 seconds, the countdown resumed as planned. At 9:42:26.546 AM EST, Gemini 11 lifted off just a half a second into its two-second launch window and started its chase. After five minutes and 36 seconds of powered fight, the second stage of GLV-11 shutdown. Twenty seconds later, the 3,798-kilogram Gemini 11 spacecraft (the heaviest of the series) separated from its spent launch vehicle.

 

The Fastest Rendezvous Ever

Although he had been warned not to look out his window, Dick Gordon could not help but take his eyes off the instruments and admire the view of the sunlit debris engulfing the spacecraft following stage separation for just an instant. Making sure they had their spent booster in sight in order to avoid a collision, Conrad performed the IVAR maneuver twenty seconds after separation using information from their onboard navigation computer. With this first maneuver completed, Gemini 11 was now in a 161 by 279.6 kilometer orbit 430 kilometers away from its Agena target. The chase was on!

While making their first pass over Africa and out of contact with ground controllers, Conrad made the next maneuver of one meter per second about 23 minutes after orbit insertion to align the plane of Gemini’s orbit with that of the GATV. Conrad then turned Gemini’s nose forward and up 32° above the local horizontal. Upon activating the onboard radar, the Agena’s transponder was detected at a range of 93 kilometers. Once back in touch with ground controllers for a navigation update, the crew learned that their launch was a half a second late putting them about 3½ kilometers behind where they thought they were. This minor dispersion would be cancelled out during subsequent maneuvers.

With the onboard and ground calculations now showing virtually identical results, the crew stuck with their computer’s figures and proceeded with their rendezvous. At a mission elapsed time of 49 minutes and 58 seconds as Gemini 11 was approaching its first apogee near Australia, the crew began its Terminal Phase Initiation maneuvers while 18 kilometers below and 28 kilometers behind the Agena. As Gemini 11 continued to approach the Agena, the spacecraft broke into orbital dawn 16 minutes later than planned due to the unscheduled hold during launch. As a result, the lighting was not as optimal as had been planned at this phase of the rendezvous leaving Conrad and Gordon scrambling for their sunglasses to keep their target in sight. As the two spacecraft were approaching the coast of California, Conrad fired the OAMS to slow Gemini to a stop just 15 meters from the Agena. Only 85 minutes after launch, Gemini 11 had completed its rendezvous meeting the primary objective of the mission after expending only 44% of its 426-kilogram OAMS propellant load.

After receiving permission from ground controllers, Conrad then proceeded to dock with the Agena GATV at a mission elapsed time of one hour, 43 minutes and 16 seconds. Once completed, the two astronauts then conducted more docking exercises with each astronaut taking turns redocking the Gemini and Agena a total of four times in both light and darkness. Conrad and Gordon then started working on their experiments. About three hours after docking, Conrad fired the Agena’s main engine for six seconds for a 33 meter per second velocity change to adjust the orbital plane and test the engine for the big burns to come later on. By 6:00 PM EST, the astronauts finally began their well deserved first sleep period of their mission.

 

The First EVA

The astronauts first full day in orbit would be dominated by the first EVA of the mission. Four hours before the scheduled beginning of Dick Gordon’s EVA, the two astronauts began preparing their equipment. After endless rehearsals on the ground, they found themselves virtually ready to go much more quickly than planned and contemplated starting the EVA a revolution early. Instead, it was decided to stick with the schedule so they sat and waited. After a last minute scramble to get Gordon’s sun visor attached to his helmet followed by a brief rest, the hatch was opened at mission elapsed time of 24 hours and two minutes. After disposing of some unwanted garbage bags, Gordon then proceeded to attach a handrail to help him maneuver outside during the EVA. He then proceeded to retrieved the S-9 Nuclear Emulsion experiment mounted on the exterior above Conrad’s door and install, with some difficulty, a camera to monitor his own movements.

After a couple of attempts, Gordon was able to work his way down to Gemini’s nose with Conrad helping out with the umbilical line. Gordon used hand rails to turn himself and sit astride of the spacecraft’s nose. As Conrad shouted “Ride ‘em, cowboy!”, Gordon tried wedging his feet between Gemini’s nose and the TDA docking cone in order to perform his next tasks. Unfortunately while this tactic to steady himself worked during simulated zero-g training in aircraft, Gordon had difficulties maintaining position in orbit and spent six minutes trying to attach the 30-meter tether to Gemini’s docking bar as would be needed during the tethered stationkeeping exercise later in the mission.

At this point Gordon was overheating with sweat stinging his eyes and affecting his vision. As Gordon struggled back towards the hatch to retrieve the HHMU and address the next EVA objective, Conrad began to question whether his pilot, exhausted by constantly struggling against his stiff pressure suit, should continue. As had happened during the earlier umbilical EVAs, tasks took much longer and were more difficult than had been anticipated. Finally, Conrad decided to cut the EVA short and got Gordon back inside. The hatch was closed only 33 minutes into what was suppose to be a 107-minute EVA. Neither the HHMU nor the power tool would be used during this EVA after all.

After resting and removing unneeded EVA hardware, they opened the hatch 25 hours and 35 minutes into the mission and discarded all the loose gear that was no longer needed. Learning from past experience, flight planners had scheduled light activities after the EVA to allow the astronauts some time to rest. Conrad and Gordon spent time leisurely stowing equipment and getting their small cabin back in order. The crew ate, took photographs of airglow and performed periodic systems as well as medical checks. Finally, the crew started their second sleep period at 5:12 PM EST some 31½ hours after launch.

 

The Busy Day

After getting about 7½ hours of sleep, Pete Conrad and Dick Gordon skipped breakfast and immediately began preparations to light the Agena’s main engine. Although there was a last second issue with Agena’s onboard displays, at 1:12 AM EST on September 14, the Agena main engine was ignited at a mission elapsed time of 40 hours and 30 minutes. The 26-second burn increased the combined spacecraft’s velocity by 279.6 meters per second as it threw the crew against their restraints pulling about one negative-g. “Whooped-de-do!”, Conrad exclaimed about the experience, “the biggest thrill of my life!”. As Gemini 11 soared towards a record setting 1,373-kilometer apogee, the crew began taking he first of a total of more than 300 photographs of the Earth below.

The orbit was carefully chosen so that the apogee would be in the southern hemisphere near Australia where the radiation exposure from the somewhat asymmetric Van Allen belts would be minimized. Gordon reported that his dosimeter was reading only a modest 0.2 rads per hour. More detailed post-flight examination of the crew’s radiation exposure showed that it was less than expected. After completing two revolutions in its extended 289 by 1,373 kilometer orbit, Conrad fired the Agena’s main engine for a third time to slow down the combine spacecraft by 280 meters per second and lower the apogee down to 304 kilometers.

According to the schedule, Conrad and Gordon were immediately to start preparations for the mission’s standup EVA. Instead, they opted to take their first meal break of their second full day in orbit. With plenty of time to prepare, they were ready to start their second EVA on schedule opening the hatch while passing over Madagascar at a mission elapsed time of 46 hours and 7 minutes. Using just a short tether which kept his feet firmly on the cabin floor, Dick Gordon had both of his hands free to perform his assigned tasks.

Gordon was able to easily mount the cameras he needed to use during the EVA and performed his other tasks at an almost leisurely pace which he described as “most enjoyable”. During the two nighttime passes of the EVA, Conrad aimed the nose of the spacecraft with Gordon’s direction so that the S-13 Ultraviolet Astronomical Camera could take its photographs of the prescribed targets. During the day passes, Gordon continued snapping photographs of the Earth below. Unlike many earlier EVAs, the pace of this one was much more relaxed with both Conrad and Gordon even catching a brief catnap while waiting for the second orbital sunset!

Having completed his assigned tasks as the second orbital dawn approached, Gordon slipped back into his seat and closed the hatch after just over two hours. While the astronauts were tired, it was more from the level of mental concentration required to perform their experiments rather than the extreme physical exertion of the earlier umbilical EVA. The crew rested and then began preparations for the tethered stationkeeping exercise with the Agena.

While over Hawaii at a mission elapsed time of 49 hours and 55 minutes, Conrad unlatched the Agena with its main engine pointed towards the Earth and gently backed off as the tether connecting the two spacecraft unfurled. The tether briefly became stuck about the halfway point but was freed with a jerk after Conrad pulsed the OAMS thrusters. The tether then got hung up on a Velcro pad on the Agena but Conrad was able to use his thrusters to move it and pull it free. The disturbances from the tether deployment made it more difficult for the two spacecraft to settle in an initial gravity gradient orientation as planned. Engineers had expected the Agena to stabilize after only seven minutes. When this failed to happen, the decision was made to move on to spin up the tethered spacecraft for the next phase of the test.

After the initial firing of the thrusters to spin up the combination to 38° per minute, the tether began moving like a skipping rope.  As this motion damped itself out, Conrad was eventually able to get the spin rate up to 55° per minute. While neither crew member could feel anything, they placed a loose camera in front of themselves and noted that it moved straight to the back of the cabin – the spinning Gemini 11 and Agena GATV-5006 were creating artificial gravity in orbit for the first time. After four hours of tethered operations, Conrad jettisoned the Gemini’s docking bar to which the tether was attached and backed gently away from the Agena.

The mission plan had called for Conrad to slow down Gemini 11 so that it would enter a lower orbit and pull ahead of the Agena. But since the original rendezvous and the tethered stationkeeping exercise had consumed much less OAMS propellant than planned, it was decided to add a second rendezvous exercise in the time remaining in the mission. The Gemini 11 crew were instructed to perform a “coincident orbit” or “stable orbit” rendezvous where they would perform long range stationkeeping at a distance of 30 kilometers followed by a move to closer range.

Conrad fired the OAMS thrusters to place Gemini 11 in a slightly higher orbit allowing the Agena to move ahead. Three quarters of an orbit later, Gemini 11 was moved back into the same orbit as the Agena but 30 kilometers behind. Conrad and Gordon then conducted additional experiments including the D-15 Night Image Intensification which they apparently enjoyed as they viewed the night side of the Earth and their GATV with its blinking lights in the distance. The crew then settled in for their mission’s last sleep period ending a very busy day in orbit.

 

One Last Rendezvous and The Return Home

After waking up early in the morning of September 15, Conrad and Gordon discovered that Gemini 11 had drifted 46 kilometers behind the Agena GATV. At a mission elapsed time of 65 hours and 27 minutes, Conrad fired the OAMS thrusters to place Gemini 11 into a lower orbit in order to catch up with their target for the last time. Between maneuvers, Conrad and Gordon finished up their remaining experiments. An hour and 13 minutes after the day’s first maneuver, Gemini 11 had caught up with its Agena GATV and took up station some distance away to stay clear of the tether which Gordon noted was swinging about as a result of Gemini’s thruster firings. Conrad quipped that ground controllers should send up a tanker to refuel their craft and continue work. But of course this was not in the cards. With this bonus rendezvous exercise completed, Conrad fired the OAMS thrusters to slow the craft by about a meter per second and leaving the Agena behind for the last time. As in earlier missions, the Agena would be used for some additional engineering tests and eventually be left in a 352-kilometer orbit where it could be used as a rendezvous target in a future mission.

As Conrad and Gordon prepared for their return to Earth, there was only one mission objective left to accomplish: an automatic precision landing under computer control. Because of the design of the Gemini capsule, it generated an appreciable amount of lift during reentry allowing it to be steered up to 550 kilometers downrange or 50 kilometers cross range. Earlier Gemini missions had typically been steered manually using inputs from the navigation computer for guidance but this time the trip home would be hands off.

At mission elapsed time of 70 hours and 41 minutes, Gemini 11 fired its four solid retrorockets to begin its half hour descent back to Earth. Once the reentry interface was reached at an altitude of 120 kilometers, Gemini’s computer turned and banked the reentry module to keep it on target. The automated system worked flawlessly using less attitude control propellant than expected as the Gemini 11 reentry module came down only 6.4 kilometers from its aim point. The capsule splashed down in the Atlantic only 4.6 kilometers from the Iwo Jima-class amphibious assault ship, the USS Guam, after a flight lasting 71 hours, 17 minutes and 8 seconds. Conrad opted for a helicopter pickup so he and Gordon were on the USS Guam 24 minutes after splashdown. Their reentry module was recovered and on board the recovery ship a half an hour later.

With the mission of Gemini 11 successfully completed, Pete Conrad and Dick Gordon began a long series of medical exams and debriefings. They had shown that the M=1 rendezvous preferred by Apollo mission planners was practical. They also showed that a computer controlled reentry and precision landing was possible – another important demonstration for the Apollo missions. Unfortunately, there were continuing problems with astronaut fatigue during EVA which desperately need to be resolved. With only a single Gemini mission remaining in the program which had to be wrapped up no later than the end of January 1967, the crew of Gemini 12 had their work cut out for them before Apollo could send astronauts to the Moon.

 

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Related Video

Here is a short NASA documentary from 1966 summarizing the Gemini 11 mission.

 

 

Here is a 1968 NASA documentary which gives an excellent overview of the technical details of the lunar orbit rendezvous techniques developed for Apollo.

 

 

Related Reading

“Gemini 10: Dual Rendezvous in Space”, Drew Ex Machina, July 18, 2016 [Post]

“The Angry Alligator & The Snake: The Mission of Gemini 9”, Drew Ex Machina, June 6, 2016 [Post]

 

General References

David Baker, The History of Manned Space Flight, Crown Publishers, 1981

Barton C. Hacker and James M. Grimwood, On the Shoulders of Titans: A History of Project Gemini, SP-4203, NASA History Division, 1977

David J. Shayler, Gemini: Steps to the Moon, Springer-Praxis, 2001

“Gemini 11 Press Kit”, NASA Press Release 66-226, September 2, 1966